The invention relates to electrical circuit arrangements and more specifically to electrical circuit arrangements for producing variable frequency outputs.
Electrical circuit arrangements for producing variable frequency outputs are known in the form of phase locked loops in which a variable frequency voltage-controlled oscillator (VCO) feeds a phase comparator via an adjustable divider having a division factor of N. The phase comparator compares the phase of the divided frequency with the phase of a reference frequency, and adjusts the VCO to produce phase equality. The VCO frequency (the output of the arrangement) can therefore be adjusted in steps each equal to the reference frequency by making unit changes in the division factor.
The disadvantage of such an arrangement, however, is that the minimum step change possible in the output frequency is the same size as the reference frequency.
An object of the invention, therefore is to provide an improved electrical frequency control arrangement.
A more specific object of the invention is to provide an electrical frequency control arrangement incorporating a phase locked loop in which a variable frequency voltage-controlled oscillator feeds a phase comparator via an adjustable divider, in which the VCO frequency can be adjusted in smaller steps than the reference frequency. It is also an object of the invention to provide, in such a frequency control arrangement a loop bandwidth greater than the step size with good spurious performance and without using close tolerance components.